PROJECT SUMMARY/ ABSTRACT Basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and squamous precancers in-situ (CIS, also known as actinic keratoses), are the most common of all human neoplasias and contribute significantly to the national healthcare burden. While existing techniques such as cryoablation or surgical excision are generally curative, those treatments cause scarring that can be especially disfiguring in patients at high risk for skin cancer (i.e., patients with chronic severe photodamage; immunosuppression due to organ transplantation; or Basal Cell Nevus Syndrome, BCNS). Photodynamic therapy (PDT) combines a photosensitizer (protoporphyrin PpIX, induced by the administration of aminolevulic acid, ALA) with activation by visible light, and is a completely nonscarring technique. PDT is approved by the FDA for field treatment of widespread cutaneous precancers, and in European countries PDT is also approved for treating SCC and BCC. In the U.S. however, approval of PDT for SCC and BCC will require further clinical trials to demonstrate an efficacy similar to existing techniques (destructive ablation). As a new way to increase PDT efficacy, we showed that in animal models of SCC and BCC, transient administration of Vitamin D (VD) prior to ALA-PDT enhances PpIX accumulation and PDT efficacy. The oral (dietary) form of VD (cholecalciferol; D3, given as 10,000 IU/day for 10 days) increases PDT-induced tumor killing by several fold, and is very safe with little risk for inducing hypercalcemia. In this grant, we propose to test this approach in human clinical trials using oral D3 as a neoadjuvant to PDT. Aim 1 will examine the relationship between VD status (serium 25OH-D3) and PDT efficacy for CIS. Subaim 1a is a longitudinal study to test the correlation between serum 25OH-D3 levels and treatment outcomes in routine PDT patients in our clinics, and to examine the predictive value of certain biomarkers (e.g. VDR allelic polymorphisms). Subaim 1b is an interventional trial to assess the benefit of giving neoadjuvant D3 (transient oral D3) prior to PDT. Results from combined D3/PDT treatment (Subaim 1b) will be compared to results after D3 alone (Subaim 1a), stratified by the VD deficiency status. In Aim 2, we will examine the potential benefit of neoadjuvant D3/PDT in patients with BCNS (Gorlin-Goltz syndrome). These patients, who have multiple BCC tumors will receive 3 bimonthly PDT treatments, and rates of tumor shrinkage will be correlated with serum 25OH-D3 levels. Each patient will serve as his/her own control by randomizing the order of the first two PDT treatments, one session to be done with neoadjuvant D3 and the other without. The third PDT treatment will occur after the serum VD level has been adjusted to normal levels with D3 supplements. This approach will allow us to determine whether neoadjuvant D3/PDT can help all patients, even the VD deficient individuals, through customization of D3 dose. Together, we expect this group of clinical trials to establish the foundation for a new treatment modality, i.e., neoadjuvant D3/PDT for skin cancer. The potential benefit for public health is that data showing improved efficacy of PDT with this safe and simple approach will lay the foundation for a nonscarring alternative to surgery for early SCC and BCC tumors.